Cleaning the Air We Breathe - Controlling Diesel Particulate Emissions from Passenger Cars

The mechanism of formation of particulate matter (PM) in the diesel engine combustion process is outlined, and the increasingly stringent PM emissions limits in current and projected environmental legislation are noted in the context of the increasing use of fuel-efficient high-performance diesel engines in passenger cars. The types of filter systems for abating diesel particulates are described, as are the principles of filter regeneration - the controlled oxidation of PM retained in the filter, to prevent an accumulation which would ultimately block the filter and degrade engine performance. PM is characterised in terms of both particle size (coarse, accumulation mode, and nucleation mode nanoparticles) and chemical composition, and the filtration issues specific to the various PM types are outlined. Likely future trends in filter design are projected, including multifunctional systems combining PM filtration with NOx control catalysts to meet yet more stringent legislative requirements, including European Stage 5 and 6, and the so called 'Bin 5' levels in the U.S.A.